The present invention relates to a steering system for motor vehicles having a normal operating system, as well as an emergency operating system which automatically becomes active in response to a malfunction of the afore-mentioned system. The normal operating system includes a steering-angle setpoint generator that is actuatable by a steering handle, in particular by a steering hand wheel, a steering-angle actual-value sensor, or position feedback encoder, actuated by steered vehicle wheels, a motorized control unit controlling the steered vehicle wheels, as well as a control system which controls the control unit in accordance with a setpoint-actual value comparison of the steering angle. Between the steering handle and the steered vehicle wheels, the emergency operating system includes a mechanical and/or hydraulic positive coupling which is active at least in response to emergency mode.
Steering systems of the aforementioned type, in which the xe2x80x9csteer-by-wirexe2x80x9d concept is implemented, are fundamentally known and are being further developed with substantial outlay to facilitate series production in the near future.
To date, two lines of development have been pursued.
In accordance with the one development line, in the event of a malfunction of the normal operating system, which is continually monitored for correct operation, a hydraulic or mechanical positive coupling between the steering handle and steered vehicle wheels, which is inactive during normal mode, is switched into action. Thus, in the event of emergency mode, an, in theory, conventional steering is at hand.
The other development line provides for an optionally multiply redundant configuration of the normal operating system, in order to ensure adequate safety under all conceivable operating conditions.
It is an object of the present invention to provide a steering system which is distinctly improved from the standpoint of safety.
The above and other beneficial objects of the present invention are achieved by providing a steering system as described herein. According to one example embodiment of the present invention, a steering system of the type mentioned at the outset includes an auxiliary system, which is at least substantially redundant relative to the normal operating system and which, in response to malfunctions in the normal operating system, automatically becomes or remains active and, in a transitional phase, adapts the operating characteristics of the steering system to the operating mode of the emergency system, which becomes active when the transitional phase comes to an end or when the adaptation has been effected.
The present invention is based on the realization that the systems described at the outset are still deficient as far as safety is concerned.
The normal operating system, which functions without any positive coupling between the steering handle and steered vehicle wheels, routinely exhibits clearly different operating characteristics than those of the emergency operating system working with positive coupling. This may be due, for example, to the normal operating system having a steering angle transmission ratio which deviates from that of the emergency operating system, between the adjusting displacement of the steering handle and the associated steering angle variations of the steered vehicle wheels. Moreover, the normal operating system may function in dependence upon parameters, in such a way that, in response to critical driving states, automatic steering corrections are undertaken largely without the driver""s involvement. If the need arises, at this point, to switch on the emergency operating system at an instant when the normal operating system is working with a steering angle transmission ratio that deviates considerably from that of the emergency operating system or when it seeks to perform an automatic steering correction, the driver may suddenly be overwhelmed, since he/she may steer the vehicle using only the emergency operating system.
Operating systems, which, due to multiple redundancy, are able to maintain the habitual operating characteristics of the steering system, even in an emergency, encourage the driver to ignore possible malfunction indications for a length of time. The result, therefore, for an extended period of time, is merely a system having diminished or even no redundancy, so that each additional malfunction entails a substantial safety hazard.
The present invention is based on the general idea that, in the event of a malfunction of the normal operating system, one switches over, with a time delay, to an emergency operating system that is quite safe, the driver being given the opportunity during the time delay, to get used to the performance characteristics of the emergency operating system, in that the performance characteristics of the steering system continuously approach those of the emergency operating system.
In accordance with the present invention, the auxiliary operating system, which is provided for carrying out the transitional phase and is designed to be at least substantially redundant relative to the normal operating system, carries on the function of the normal operating system for a limited time only, approximately up until completion of an autonomous steering intervention or engagement previously initiated by the normal operating system. Then, it gradually familiarizes the driver more and more with the operating mode of the emergency operating system.
The present invention utilizes the redundancy given by the normal operating system and the auxiliary operating system, in a completely new way, namely to make the transition to an extremely safe emergency operating system.
On the one hand, this arrangement ensures that the driver notices a malfunction of the normal operating system. On the other hand, the driver is prevented from being dangerously surprised when the emergency operating system is switched on.
One example embodiment of the present invention provides for the normal operating system to also control a manual-torque simulator, so that the driver senses a steering resistance, as in the case of a conventional steering operation. In this connection, it is provided in the transitional phase for the auxiliary system to gradually switch the manual-torque simulator more and more over to the manual torque of the emergency operating system so as to avoid an abrupt change in the manual torque when the emergency operating system is ultimately switched on.
In addition, it may be provided in the transitional phase for the auxiliary system to adjust the steerable vehicle wheels and the steering handle relatively to one another such that, given an active emergency operating system, the steering handle assumes a middle, i.e., normal position in the straight-ahead position of the steerable vehicle wheels.